The present invention is directed to a method for producing a semiconductor laser device having a pair of closely spaced semiconductor lasers in order to achieve interlaser spacings of approximately 2 .mu.m. Such a device may be incorporated in numerous devices including optical disk readers or flying spot scanners (commonly referred to as raster output scanners (ROSs)). A flying spot scanner typically has a reflective multifaceted polygon mirror that is rotated about its central axis to repeatedly sweep one or more intensity modulated beams of light across a photosensitive recording medium in a linear or fast-scanning direction. Printers employing multiple intensity-modulated beams are referred to as multibeam or multispot printers. In such printers the dual lasers are considered to be an enabling technology for high speed operation at resolutions of about 600 spots per inch (spi). The present invention utilizes integrated alignment devices which are formed on the surfaces of the semiconductor wafers from which the laser diode dies are produced to accurately position a pair of laser dies with respect to one another. Furthermore, a small air space generally separating the two laser dies provides thermal, electrical and optical isolation therebetween.
The desirability of a multiple beam semiconductor laser has been recognized previously. However, because of thermal crosstalk between closely spaced laser diodes, practical interlaser spacings have generally been limited to spacings of at least 100 .mu.m. Designs intended to achieve close spacing of the emitted laser beams are known, of which the following disclosures which may be relevant:
Kato et al., U.S. Pat. No. 4,901,325, issued Feb. 13, 1990 PA1 Thornton U.S. Pat. No. 4,870,652, issued Sep. 26, 1989 PA1 Connell et al., U.S. Pat. No. 4,796,964, issued Jan. 10, 1989 PA1 Hakamada, U.S. Pat. No. 4,403,243, issued Sep. 6, 1983 PA1 forming a pair of laser dies with one of the laser dies having an alignment member on a surface thereof and the other of the laser dies having a complementary alignment member on a surface thereof; and PA1 assembling the pair of laser dies with the alignment members on each of the laser dies mating with one another so as to space opposed surfaces of the laser dies from one another and align the dual beam semiconductor laser. PA1 producing a plurality of laser dies on a semiconductor wafer, said laser dies each including a p-n junction lying beneath a first surface of the wafer and above a substrate layer which establishes a second surface, and a first metal layer on the first surface of the wafer, thereby providing electrical contacts for the laser dies; PA1 depositing a spacer material layer over the first metal layer on the first surface of the wafer; PA1 selectively removing portions of the spacer material so as to produce complimentary alignment structures on the first surface of each laser die; PA1 depositing a second metal layer so as to metalize the surfaces of the alignment structures present on the first surface; PA1 dividing the semiconductor wafer into individual laser dies; and PA1 assembling a first die and a second die, with the first surfaces of both dies spaced apart from one another by the complimentary alignment structures, so that the alignment structures on the first die mate with complimentary alignment structures on the second die, thereby aligning the dual beam semiconductor laser.
The relevant portions of the foregoing patents, hereby incorporated by reference for their teaching, may be briefly summarized as follows:
U.S. Pat. No. 4,901,325 teaches a semiconductor laser device used in an optical disk device which utilizes a pair of semiconductor laser chips and a fixing device for fixing the laser chips so that the electrode surfaces are approximately parallel and opposite to each other. The fixing device comprises either a single-piece, U-shaped block or, alternatively, a pair of blocks, upon which the photodiodes are ultimately mounted. When a pair of blocks are used, a tooling system (see FIG. 9) is used to align and permanently affix the blocks to a base plate under the control of a vision system which enlarges and processes an image region centered on the active regions of the lasers affixed thereto.
U.S. Pat. No. 4,870,652, discloses a monolithic high density array of independently addressable semiconductor lasers. The lasers are further characterized as having emitters on closely spaced, 3-10 .mu.m, centers, without displaying phase locking and with minimal crosstalk effects. The monolithic, independently addressable array is suitable for use with high speed laser printers, laser disk technology, and fiber optic communication.
U.S. Pat. No. 4,796,964 describes a method for using a multiple emitter solid state semiconductor laser in a raster output scanner. The overlapping beams are sequenced in ON/OFF operation to avoid any inter-beam interference in a manner that assures that only one laser beam will be on at any given time. Hence, nonuniformity caused by optical interference of overlapping beams is prevented without the need for further modification of the optical properties of the beams (e.g., polarization and wavelength).
U.S. Pat. No. 4,403,243 teaches a laser apparatus including support and soldering means for a light transmitting member which is affixed so as to allow transmission of an emitted laser beam generated within the apparatus by a semiconductor laser. The light transmitting, by soldering, becomes hermetically sealed to a support member, thereby completely encapsulating the laser source.
In accordance with the present invention, there is provided a method of fabricating a dual beam semiconductor laser, including the steps of:
In accordance with another aspect of the present invention, there is provided a dual beam laser diode comprising a first laser die including a light emitting region; a second laser die including a light emitting region; and means, interposed between said first laser die and said second laser die, for spacing said first laser die from said second laser die and aligning the respective light emitting regions thereof.
In accordance with yet another aspect of the present invention, there is provided a dual beam laser diode prepared by a process comprising the steps of: